3.1.4. Azure Extended Network

Migrating a server to Azure normally means it gets a new private IP address, which is fine until something hard-coded depends on the old one. Azure Extended Network stretches an on-premises subnet into Azure so that a migrated VM keeps its original IP address.

How it is built:

• A pair of Windows Server machines running the Azure Extended Network agent, one on-premises and one in Azure, act as the two ends of the stretched subnet.
• They communicate over an existing site-to-site VPN or ExpressRoute connection — Extended Network does not create hybrid connectivity, it rides on top of it.
• The Azure side of the stretched subnet lives in a virtual network you already own.

⚠️ Exam Trap: Extended Network is a migration aid, not a design goal. It exists to buy time for applications with hard-coded addresses. The exam scenario that calls for it always names the constraint explicitly: the workload must move but the IP address cannot change.